The present invention relates to a packet communication quality measurement method and system and, more particularly, to a packet communication quality measurement method and system in which probe packets are exchanged between two quality measurement apparatuses connected via a packet communication network, thereby measuring the packet communication quality between these quality measurement apparatuses on the basis of the transmission/reception status.
A conventional packet communication quality measurement method which measures various parameters including the packet delay distribution (delay time), packet loss (loss factor), and throughput (data transfer amount per unit time) as the communication quality of a packet communication network adopts two quality measurement methods: passive and active measurement methods.
According to the passive measurement method, a packet which passes through a desired node or link within a packet communication network is monitored, and the quality of the packet communication network is calculated from the monitoring result (see, e.g., Japanese Patent Laid-Open No. 2001-53792). To obtain a packet delay distribution by the passive measurement method, e.g., temporarily synchronized quality measurement apparatuses are arranged at the two ends of a desired path to be measured. Packets actually transmitted/received by the user via the path, i.e., user packets are captured by the quality measurement apparatuses. Pieces of header information and packet detection times which can specify the user packets are acquired as monitoring data. Two monitoring data obtained by the quality measurement apparatuses are matched with each other. The packet detection time difference of a single user packet is calculated to acquire the packet delay time on the path. The packet delay times of respective user packets are statistically processed to attain a packet delay distribution.
According to the active measurement method, an agent which transmits many probe packets periodically or in accordance with a pseudo user packet generation pattern and an agent which receives the probe packets are arranged within a network, and the network quality between the agents is estimated from the communication qualities of the probe packets (see, e.g., Japanese Patent Laid-Open No. 62-176239). To obtain a packet delay distribution by the active method, e.g., temporarily synchronized quality measurement apparatuses are arranged as the above-mentioned agents at the two ends of a desired path to be measured. A plurality of probe packets are exchanged between the quality measurement apparatuses via the path. The transmission and reception times of each probe packet are acquired as monitoring data. Two monitoring data obtained by the quality measurement apparatuses are matched with each other. The packet transmission/reception time difference of each probe packet is calculated to acquire the delay time on the path. The packet delay times of respective probe packets are statistically processed to attain a packet delay distribution.
These conventional packet communication quality measurement methods suffer the following problems in measuring the quality.
To measure the one-way delay of a packet flowing in a desired direction, in the passive measurement method, many user packets passing through two temporarily synchronized points are compared with each other, as described above. However, the presence of user packets having the same contents causes erroneous packet recognition which decreases the measurement precision, or increases the calculation amount because an enormous amount of data must be processed. For this reason, the passive measurement method is poor in scale extensibility.
To measure the round-trip delay, in the passive measurement method, one-way delays are combined, or a time taken for Ack (Acknowledge) of TCP (Transmission Control Protocol/Internet Protocol) to return is measured. The former method has the same problem as that of one-way delay measurement. In the later method, processing by a server apparatus which performs TCP communication is needed up to the TCP layer, resulting in a large processing delay and low delay precision. Furthermore, measuring the loss factor requires a large calculation amount because pieces of traffic information at a plurality of portions are collated with each other.
According to a method of transmitting a probe packet in accordance with a pseudo user packet generation pattern by the active measurement method, many probe packets flow separately from user packets, applying a load to the packet communication network. At this time, the network load becomes equal to an increase in the number of users, and increases to a non-negligible degree. In a method of transmitting a probe packet at a predetermined interval by the active measurement method, the obtained communication quality is a probe packet communication quality, which is not always a user packet communication quality.
When probe packets are transmitted at a predetermined interval, the traffic of supplying each probe packet is not always constant, and results different from an actual communication quality are observed. For example, the delay amount is measured for several days by transmitting probe packets every other minute to a channel which exhibits no traffic (traffic amount=0) and the delay amount=1 serving as a delay measurement result in the morning, and the traffic amount=1 and the delay amount=100 in the afternoon. In this case, the delay amount=1 is measured by 50% of all probe packets transmitted during this measurement period, the delay amount=100 is measured by the remaining 50% of the probe packets, and the average delay amount is 50.5. On this channel, however, the traffic is generated in the afternoon, and an actual delay amount is 100. Thus, measurement results different from an actual communication quality are observed. This problem cannot be solved even by infinitizing the measurement period.